There are more than fifty types of glaucoma. Many are rare. All cause a similar pattern of damage to the optic nerve but differ in the underlying mechanism. The commoner types of glaucoma are mentioned below. Examination of the eye may detect another condition such as pigment deposition, crowding of structures at the front of the eye or a congenital anomaly to explain the increased pressure and requiring specific treatment.
Chronic Open Angle Glaucoma is by far, the commonest type. The term ‘chronic’ denotes a condition that develops slowly, over many years and ‘open angle’ indicates that the iris (the coloured part) does not obstruct fluid leaving the eye through the meshwork tissue that rings the periphery of the cornea (the clear window) on the inside. Eye examination reveals no reason for the pressure to be elevated. In a common variant, glaucoma develops even though eye pressure measures in the usual range and it is postulated that reduced blood supply or structural weakness of the optic nerve head in these eyes may predispose to glaucoma damage at lower levels of pressure stress. The term ‘Normal Pressure Glaucoma’ is falling out of use for this type of glaucoma because increasingly it is considered to be on the same spectrum.
Angle Closure Glaucoma tends to occur in naturally smaller (usually long-sighted) eyes, in which the angle space between the iris and the cornea is very narrow. The exit of fluid from the eye is impeded by the iris, causing eye pressure to rise.